This application claims the priority of PCT document PCT/EP00/02815 filed Mar. 30, 2000 and German patent document 199 18 995.1 filed Apr. 27, 1999, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a steering and braking system for a vehicle.
European patent document EP 07 54 611 A1 discloses a drive-by-wire steering and braking system which has a multiple partially redundantly configured system components such as arithmetic units and actuators for controlling the steering and the service brake of the vehicle as a function of variables measured by sensors, according to defined control laws. The sensor signals are firstly fed to an arithmetic unit with three synchronously operating arithmetic devices which generate actuating signals that are fed via a communications device (data bus) to vehicle modules, each its own power supply and final positioning elements for the brake, steering, suspension and drive. The communications device is, like the arithmetic unit, of redundant configuration and comprises in total three data buses. The power supply of the system is also provided redundantly.
One object of the invention is to provide a steering and braking system of the type described above, which is reliable, fault-tolerant and of simple design.
This and other objects and advantages are achieved by the steering and braking system according to the invention, which includes a distributed control loop with an arithmetic unit for generating set point signals and a regulator unit for generating actuator signals for the actuators. The arithmetic unit, the regulator unit and a state-determining device in which state signals describing the current vehicle situation are determined or generated are connected to one another by a data bus in which signals are successively transmitted between the various units and/or devices at defined time intervals. The signals of the devices and units are combined in cycles, one complete set of information being capable of being transmitted via the data bus in each cycle.
According to the innovation, within a single cycle the signals of the various units and devices are generated in a specific series or sequence, and transmitted via the data bus; in particular, in the sequence: arithmetic unitxe2x80x94state-determining devicexe2x80x94regulator unit. Accordingly, in each cycle, set point signals for steering and/or brake are first generated in the arithmetic unit and transmitted via the data bus; then signals describing the vehicle state are generated in the state-determining device and transmitted via the bus; and finally the actuating signals for the actuators are generated in the regulator unit and also transmitted via the data bus. Each of the components comprising the arithmetic unitxe2x80x94state-determining device and regulator unit can form the starting point of the sequence without changing the sequence itself. Instead of the series: arithmetic unitxe2x80x94state-determining devicexe2x80x94regulator unit, it is therefore also possible to have the series: state-determining devicexe2x80x94regulator unitxe2x80x94arithmetic unit, as well as regulator unitxe2x80x94arithmetic unitxe2x80x94state-determining device. These series have equal value to one another.
Because the data bus connects all the devices and units of the steering and braking system to one another, it is ensured that the signals of one unit or device are available to all the other components of the system. The defined sequence: arithmetic unitxe2x80x94state-determining devicexe2x80x94regulator unit ensures that, first of all in the arithmetic unit, the set point signals are generated which may be required in the state-determining device, and at least in the regulator unit in which a set point/actual value comparison is carried out in order to generate actuating signals. The signals generated in the state-determining device are also required in the regulator unit for generating the actual signals and/or actuating signals for the actuators of the brake and of the steering.
On the other hand, information on the actual state of the actuators and/or of the regulator unit itself (for example a status display from which the instantaneous operating status is apparent) can be fed by the regulator unit to, in particular, the arithmetic unit via the data bus. Because the signals of the regulator unit are generated at the end of a cycle, while the signals of the arithmetic unit are generated at the start of a cycle, the arithmetic unit can react directly to the information of the preceding signals of the regulator unit at the start of a following cycle. The information flow from the regulator unit to the arithmetic unit provides the advantage that suitable strategies for the computation of the set point values, which are adapted to the current situation, can be implemented in the arithmetic unit as a function of the state of the regulator unit and/or of the actuators. As a result, it is in particular possible to maintain the function of a faulty regulator unit or of a faulty actuator without restriction (or with only a small degree of restriction) of the functionality at an exclusively electronic level. In this manner, fault tolerance can be realized without additional mechanical or hydraulic hardware components. In addition to fault tolerance, this arrangement provides the advantage that the costs and the weight of the steering and braking system are reduced.
In contrast to the prior art devices, which are based on event control, in the present invention a timed approach is used in which actions are carried out in accordance with a predefined communications matrix at fixed times and/or in predetermined time windows (slots), each time window being assigned an action of a device or unit. The duration of a time window or the distance between two successive time windows is expediently constant.
As a result, high-speed control loops can be obtained in distributed steering and braking systems and redundant arithmetic units can be easily coupled. The timed signal transmission via the data bus in the manner of a communications matrix or of a communications schedule increases safety, improves availability and can be tested more easily for operational capability in the development phase and in quality assurance.
In one embodiment of the invention, at least some of the units and devices are of fault-tolerant, in particular redundant design. This preferably includes the arithmetic unit for generating the set point signals and the regulator unit for the steering. These units must also be fully operational for stabilizing the vehicle, even in limiting operating ranges in which high-speed, regulated steering interventions may be necessary, because otherwise there is the risk of losing control of the vehicle. A fault-tolerant design of the units relating to the steering ensures that the vehicle can be controlled even when a function fails.
On the other hand, it is not absolutely necessary for the units relating to the brake to be of fault-tolerant or redundant design. These units can, by switching them off, be placed in a fail-safe state in which faulty signals are no longer generated. Even in the event of a failure of a unit assigned to a specific wheel brake, it is possible for the brake function to be assumed by one or more of the remaining units of the other wheel brakes. Functions for chassis adjustments are carried out do not need to be made fault-tolerant or redundant either.
Redundant units and/or devices advantageously transmit and receive the signals with offset timing, which provides fault tolerance with respect to electronic interference, for example EMC interference. In the event of individual faults occurring within a time window in which the signal of a unit and/or a device is transmitted, a correct signal of the second unit or device is available in the slot with offset timing. The messages or signals of redundant units or devices are preferably transmitted in directly successive time windows, expediently within one cycle, which facilitates a matching of the redundant messages.
In one preferred embodiment, initialization signals are generated regularly in each cycle in at least one unit in the steering and braking system, and transmitted via the data bus. These initialization signals are used to initialize and synchronize the units and devices coupled to the data bus. Within one cycle, initialization signals, which increase the system""s resistance to electromagnetic interference, are advantageously generated by at least two different units. The units which generate the initializatior signals are expediently vehicle components with comparable functions, in particular regulator units (for example a multiplicity of braking regulating units) which are assigned to the different wheel brakes. In two successive cycles, the initialization signals can be generated in different units.
Two data buses are advantageously provided, signals being transmitted on the data buses permanently and synchronously within one cycle, but said signals can differ. It has proven advantageous in particular if initialization signals are transmitted in a chronologically alternating fashion on the two data buses within one cycle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.